The present application is directed to an interbody device for implantation between a pair of adjacent vertebrae in order to provide support to the vertebrae and/or promote bone fusion between the vertebrae and, in particular, to a non threaded and non cylindrical interbody device having opposed concave sides and a front to rear convex or trapezoidal configuration.
In the human spine the pad or disc between vertebrae is sometimes damaged or deteriorates due to age, disease, injury, or congenital defect. The vertebrae may also become compressed or otherwise damaged. Vertebrae often become too closely anteriorly spaced due especially to age but also other factors that generally produces an abnormal curvature with respect to lordosis or kyphosis, which is undesirable. Because of this, surgery is often utilized to place spacers or interbody devices between the vertebrae which provide proper spacing of the vertebrae and which also promote fusion between the vertebrae. When a device of this type is utilized for purposes of promoting fusion, it is often referred to as a fusion cage or an intervertebral fusion device. When utilized to promote fusion, the interbody devices sometimes are windowed or fenestrated and packed with bone fusion material to promote growth of the bone between the vertebrae. Sometimes such material is packed between a pair of devices that are placed in close proximity to one another between the vertebrae to promote growth of bone and, therefore, fusion between the vertebrae.
In the past, interbody devices have typically been either generally rectangular or cylindrical and threaded in shape. The cylindrical devices have an advantage in that they can be threadably received more or less directly between and into the adjacent vertebrae. For this purpose, the vertebrae are typically first spaced apart, and then a drill is utilized to create a partial bore (radiused channel) in each vertebra which allows this type of interbody device to be received between the vertebrae. Because of the space between the bones, the interbody device usually engages the bones only along an upper surface and a lower surface thereof. When the interbody device is of a cylindrical threaded type, the upper and lower surfaces are radiused relative to a front to rear axis and such are essentially designed to engage the portion of the vertebrae where bone is unremoved by boring to create an opening for the device.
When interbody devices are used, it is desirable that the device engages as much surface of bone as possible to provide support to the bone and to reduce the likelihood of subsidence of the device into the bone, resulting from contact pressure of the interbody spacer relative to an intervertebral surface of a vertebra, since part of the bone is somewhat spongy in nature, especially near the center of the upper and lower surfaces of the bones. The remainder of the structure mainly functions to support the two surfaces, unless the device is also used as a cage within which to pack bone fusion material. Because it is also desirable in such structures to maintain weight and volume as low as possible, in order to make the device more compatible with the body, it is also desirable to make the entire device as small and lightweight as possible, while maintaining strength.
It is also desirable to minimize the amount of cutting into and reshaping of the vertebral bones to only that which is necessary to correct the structure and function of the spine. Thus, it would be desirable to conform an interbody spacer to the shape of the intervertebral surfaces of adjacent vertebrae, which is shallowly concave, if possible in a given circumstance, rather than conform the vertebrae to the shape of the interbody spacer.
Finally, as noted above, age and injury cause the vertebrae to somewhat anteriorly collapse over time. Therefore, it is also desirable for such an interbody spacer to correctly space the vertebrae anteriorly so as to promote normal lordosis or curvature with respect to the spine.